The present invention relates to filamentary webs, i.e. non-woven webs composed of filaments rather than fibers.
More particularly, the invention relates to a method of making such filamentary webs.
The invention also relates to an apparatus for making such filamentary webs, i.e. to an apparatus for carrying out the method.
Non-woven filamentary webs, which are composed of long filaments as opposed to woven webs which are composed of short fibers, are already known per se. For example, German Published Application DE-OS No. 2,320,133 discloses a web of the type in question.
However, the prior art relating to these webs has various disadvantages. The basic web structure is defined by the longitudinally extending parallel high-strength filaments; to make the web usable as a coherent structure, these filaments must be connected with each other in direction transversely of their elongation. This is accomplished by providing one or both of the major web surfaces with transversely extending threads of synthetic plastic material; these threads are melted so as to bond with the filaments. One problem with this arrangement is the heating of the connecting threads to the requisite melting (and bonding) temperature since the required heat tends to adversely affect the strength and integrity of the filaments being connected.
Another problem is the manner of heating the threads. This is generally accomplished with the aid of two melting jaws, one or both of which are heated. If, in fact, two of these jaws are used, then the affixing of the threads to the filaments can be carried out only discontinuously. This is often unsatisfactory because it limits the operation to a relatively low production rate. A continuous operation is possible if only a single jaw is used; however, then the problem arises how to heat the threads quickly enough (i.e. within a fraction of a second) to melting temperature. Also, the prior art leaves much to be desired as to the positioning accuracy of the threads on the filaments so that the reliability of the filament connection with these meltable threads is at best uncertain.
Another prior-art approach--which is mentioned as such in the aforementioned German Published Application--suggests a woven web in which the weft consists of uncovered or braid-covered carbon filaments and the warp consists of natural or synthetic fibers. One problem with this proposal is that the final product is not as strong as the one discussed hereinbefore. Another problem is that the manufacture of this product is very expensive. The most telling disadvantage, however, resides in the fact that it is not possible to produce a web having flat surfaces. Since webs of the general kind under discussion are often used as reinforcements in thin-walled structural components--such as gliders speed boats and helicopter rotors, to name just a few--this is unacceptable.